Composite armor materials appeared during World War II as flak suits (nylon-steel) which weighed about 4.5 lb/ft.sup.3 (0.07 g/cm.sup.3). Although significant improvements therein have evolved thereafter and more particularly since the Korean War with development of lightweight non-metallic materials (ballistic nylon, fiberglass reinforced plastic), relatively lesser improvements appear to have evolved in the realm of blast protection for armored vehicles and their occupants. Combat experience has shown that tanks can readily be put out of action by blast forces from land mines. The blast defeat mechanisms attributed to land mine explosions are shock, deformation, fracture and overturn. Armor design of tank floors heretofore apparently has been based primarily only on the criterion that the armor not fracture as a result of a nominal "belly" mine blast loading. It appears that the blast induced dynamic response of the floor upon crew members and other critical operational components until more recent years has not received as much continuing attention as desirable to provide better data to evaluate and to improve tank floor armor so as to improve the overall mission survivability of tanks.
Some tank floor armor currently is made of class 2 rolled homogeneous armor plate intended for use where maximum resistance to structural failure under conditions of high rate of shock loading is required, and where resistance to armor piercing ammunition is of secondary importance. Unfortunately, the history of design related analyses and tests has been such that the majority of design information generated is based on the response of a variety of steel plates tested with unclamped edge support. Engineering design equations have been developed which predict permanent plate deformation and fracture as a function of thickness. Recent studies have shown that transient plate response can now be predicted with the aid of certain computer codes.
Until the last few years, little regard was given to the relationship between tank floor design and tank mission effectiveness. With the advent of survivability/vulnerability methodology being imposed upon combat vehicle designs, new questions must now be answered relative to component dynamic interactions within vehicles subjected to extreme explosive blast loading environments.
It has been suspected for some time that the dynamic response of tank floor armor plate was probably large enough to incapacitate the crew members even if the tank floor was not fractured. Tank crews have been found to be vulnerable from two types of tank floor-induced loadings, both of which are functions of transient floor displacement. One loading is a mechanically induced shock which can cause body damage resulting from the relative movement of the various human organs. The second loading is overpressure within the tank compartment created by the shock wave in the air generated by the tank floor deformation. This overpressure is also potentially damaging to the human organs and more particularly to the air-containing organs induced by the rapid gross relative deformation of body tissue. Obviously the tolerance limits to a shock wave are different for different parts of the body. Eardrums usually are the first to rupture, followed by damage to the lungs. It is also known that armor thickness is proportional to permanent plate deformation and that the thicker the steel plate, the better its capability to attenuate shock loads. It has been estimated that the step velocity response of the armor floor can be represented by a velocity step input of 340 ft/s (104 m/s). It is now well known that this magnitude of velocity step would readily incapacitate an unprotected tank crew member.
There is calculated speculation that an unprotected tank crew member will not survive the dynamic response attendant mine blasts which generate a step velocity change of 15 ft/s (4.6 m/s) over a duration of one millisecond. Since the dynamic response of a tank floor subjected to a mine blast is quite violent, current practice is to suspend or try to isolate the crew member off from the tank floor such as in shock-absorbing seats. This solution to the problem of crew member survivability is now being reexamined.
Crew member survivability studies and similar closely related studies directly pertinent to tanks subjected to mine blasts have been made. Shock isolation requirements that the tank crew member seats must meet if injury is to be avoided are given in various published crash design handbooks. The data reported in these references has been generated from volunteers, accident reports, and human simulators such as animals, anthropomorphic dummies, and cadavers. As might be expected, the wide variation in the physiological and psychological structure of humans precludes a simple prediction of injury that will occur as a function of shock loading. Further insight into the uncertainties associated with predicting/measuring crew member survivability has evolved. The point being made is that suspending the crew member above the floor, while desirable and potentially beneficial, does not necessarily ensure that he will not be incapacitated as a consequence of a mine blast.
It is proposed that survivable dynamic response requirements be based on the mission survivability of a tank. In this manner, the survivability of the crew member is preeminent since he is the most critical system component. Intrinsic to this approach is that the survivability of a crew member is dependent upon other critical components functioning after a land mine blast. The degradation of tank mission effectiveness can range from significant fracture of structure (such as optics) to the generation of noise in electronic circuitry. Such degradation is believed to result in greater vulnerability to enemy attack and hence lowering of crewman survivability.
If it is assumed that all critical components within a tank are of equal importance for crew member survival of a mine blast, then the survivable dynamic response design requirements are such that the tank floor armor must absorb and redistribute the blast load in a relatively mild manner. In principle this goal is considered to be achievable if space is made available to use shock isolation materials in composite structural configurations. Three particular materials tested and found to be satisfactory for use along with other materials in such novel hybrid composite armor are high strength steel honeycomb, balsa wood and a ballistic-resistant fabric, such as KEVLAR nylon.
As a consequence of this goal, it is the primary object of this invention to evolve a novel composite armor embodying novel combinations of various known media, the various combinations of which are designed not only to defeat land mine blast loadings, but also to enhance vehicular integrity against shaped charges, projectiles and irradiation.
It is a further object of the present invention to evolve the aforedescribed novel composite armor which will contribute markedly to the reduction of the highly damaging mechanical and overpressure compressive shock effect on the crewmen of tanks or other armored vehicles utilizing this novel armor.
These and other objects and advantages will become more apparent from the following more detailed description considered in conjunction with the accompanying drawing figures.